Numerical modelling of the extensional dynamics in elastoviscoplastic fluids

The extensional dynamics of an elasto-viscoplastic (EVP) fluid is studied by means of numerical simulations modelling an experimental configuration. Specifically, we track the interface between the EVP material and the Newtonian medium using an algebraic volume of fluid method (MTHINC-VOF) and employ a fully Eulerian immersed boundary method (IBM) to model the motion of the piston responsible for the extension of the material. We investigate the role of different values of the yield stress, surface tension at the interface between the EVP material and the surrounding fluid, polymer viscosity ratio, and extension rates on the necking thickness of the material, extensional viscosity, and yielding of the material for two sets of parameter with low and high elasticity. The results of the simulations reveal that when the yield stress of the EVP material is much larger than the viscous stresses, the material undergoes an elastic deformation, regardless of the selected values of the extension rate, interfacial forces, and viscosity ratio. Moreover, by increasing the ratio of the polymeric viscosity to the total viscosity of the system, the EVP material produces stronger strain hardening and reaches the minimum resolvable width sooner. Specific and novel to our study, we show that interfacial forces cannot be ignored when the surface tension coefficient is such that a Capillary number based on the extensional rate is of order 1. For large values of the surface tension coefficient, the EVP material fails sooner, with a clear deviation from the exponential reduction in the neck thickness. Moreover, our results suggest that the role of the yield stress value on the dynamics of the material is more pronounced at lower elasticity.

Automated summary

The extensional dynamics of an elasto-viscoplastic fluid is investigated through numerical simulations and experimental modeling. The study explores the effects of different factors, such as yield stress, surface tension, viscosity ratio, and extension rates, on the material behavior. The results demonstrate the importance of yield stress in determining the material's deformation, with interfacial forces also playing a significant role. The findings contribute to a better understanding of the dynamics of elastoviscoplastic fluids.